In retrieval with a keyword that is applied to, for example, retrieval of an article or a patent, or retrieval of a general Web page, a retrieval query in keyword units is used, and therefore it is not possible to include a relationship between keywords in retrieval conditions. As an example, when a user retrieves “a technology for reducing an environmental load by reducing heat radiation”, the user inputs the keywords “heat radiation, environmental load, reduce”. However, a retrieval query using these keywords includes equivocality. In this case, the retrieval query includes both of the meanings of “reduce heat radiation” and “reduce an environmental load”, and is not limited to one of the meanings. In addition, the retrieval query does not specify a relationship between heat radiation and an environmental load.
As one technology for improving retrieval accuracy is known (see Patent Document 1). A language analyzing means analyzes the language of an input retrieval request, and extracts a noun phrase including plural words and a word that is an element of retrieval conditions. A retrieval condition generating means combines the extracted words and the noun phrase by a prescribed operator, and applies a prescribed weight to each of the word and the noun phrase so as to generate a retrieval condition. A document retrieving means extracts a document matched to the retrieval condition generated by the retrieval condition generating means from the documents. A document retrieval result with a high accuracy is obtained by setting an appropriate retrieval condition on the basis of a word and a noun phrase extracted from a retrieval request input in a natural language as described above.
As another technology that improves retrieval accuracy is known (see Patent Document 2). A keyword extracting unit is included that extracts all keywords that are applicable as retrieval terms from retrieval request information that is an expression or sentence requesting retrieval. A synonym obtaining unit is included that obtains synonyms of the extracted keywords from a synonym dictionary. A document retrieval unit is included that specifies the keywords extracted by the keyword extracting unit and the synonyms obtained by the synonym obtaining unit so as to retrieve documents in the database. In addition, a retrieval result evaluation unit is included that evaluates, as a higher degree of priority, a document having a greater degree of modification similarity from among the documents retrieved by the document retrieval unit, wherein the degree of modification similarity indicates the degree of a relationship between a pair of words having a modification relationship included at least in the retrieval request information and a pair of words having a modification relationship included in the documents retrieved by the document retrieval unit. As a result, an information retrieval device is provided that retrieves information useful for a user at a high accuracy.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2001-142897
[Patent Document 2] Japanese Laid-open Patent Publication No. 2006-215717